Hi,
This seems to be an already known issue that happened (and was resolved) on Gehennas in late September, judging from another thread in here:
After handing in The True Masters 2/6, Bolvar just stands there, not giving the follow-up quest that entails talking to Katrana Prestor and then speaking to him again.
This makes finishing the attunement in time for a raid a bit difficult, so we would be thankful for a resolution. 
Hey Amy
Usually when you are to deliver a quest like this one, and the NPC is unresponsive, it is because the NPC is already engaged with another player doing the quest chain as well, so it will not interact with you.
What you need to do is to wait for the interaction with the other player ends until you will be able to deliver the quest and carry on but you can read more about this works here.
Try delivering the quest when there are less players around so you can try to be the first to interact with the NPC.
Dear Nilliarix,
That was the first thing I suspected, but after half an hour of no events involving Bolvar or the throne room, he still didn’t seem willing to talk to me. The same bug had to be fixed recently:
My quest log doesn’t contain the prequel quest (The True Masters 2/6) because I successfully handed that one in with Bolvar, but he continues to refuse giving me the follow-up (The True Masters 3/6).
EDIT: I did a command check, and the prequel quest is marked as uncompleted. Bolvar took the letter from my inventory and accepted the hand-in of the quest, but it was apparently reset instead of completed and I have to travel to Lakeshire again to get another letter.
Can you try this for me please Amy, head back to Magistrate Solomon out in Redridge Mountains and see if there is any quest available.
Just want to rule out any possibility we’re mixing up the quests. Easy to do when they are all named the same. 